Technologies for improving starting performance of high-intensity discharge lamps, such as high-pressure mercury-vapor lamps and metal-vapor discharge lamps, are disclosed in Patent Literatures 1-8, for example. Patent Literature 1 discloses enclosing a substance for improving the starting performance in the arc tube, and Patent Literatures 2-8 disclose providing the arc tube with an adjacent conductor.
As an adjacent conductor, Patent Literatures 2-6 disclose the use of a metal wire. Patent Literature 7 discloses the use of a conductive film. Patent Literature 8 discloses the use of a metal plate.
Patent Literatures 2-6, which use a wire, disclose a technology of winding a wire around a thin tube portion of the arc tube so as to form a coil (i.e. winding a plurality of times), a technology of winding a wire around the entire circumference of the thin tube portion once, and a technology of winding a wire around ¾ or ⅝ of the circumference.
Patent Literature 7, which uses a conductive film, discloses a technology of forming the conductive film on the thin tube portion of the arc tube, and connecting the conductive film and a power supply line with a metal wire.
Patent Literature 8, which uses a metal plate, discloses a technology of folding a strip of metal plate in the middle, forming concavities (i.e. curved portions) in the end portions of the metal plate which face each other due to the folding in conformity with the shape of the thin tube portion of the arc tube, and welding the facing end portions of the metal plate to each other with the thin tube portion sandwiched between the concavities.